Organic light emitting device

ABSTRACT

An organic light emitting device having a high light emitting efficiency and a long light emission lifetime is provided that comprises a pair of electrodes provided on a substrate, and a light emitting layer comprising at least one layer of an organic substance provided between the electrodes, wherein the light emitting layer comprises a first organic substance and a second organic substance mainly concerning a light emission wavelength of the light emitting layer, and wherein the first organic substance comprises a fluorine-containing organic compound.

This application is a continuation of International Application No.PCT/JP03/02693 filed on Mar. 7, 2003, which claims the benefit ofJapanese Patent Application No. 063703/2002, filed Mar. 8, 2002.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an organic thin film light emittingdevice used in a flat light source, a flat display or the like. Moreparticularly, the present invention relates to a light emitting deviceusing an organic compound, and more specifically to a device improved indurability by employing a fluorine-containing organic compound in alight emitting portion.

2. Related Background Art

Conventional examples of organic light emitting devices include a devicethat emits light when a voltage is applied to a vapor-depositedanthracene film (Thin Solid Films, 94 (1982) 171). In recent years,however, because of the advantages that formation of a large lightemitting area can more easily be attained in the organic light emittingdevice than the inorganic light emitting device, desired colors can beobtained by the development of various new materials, and the devicescan be driven at a low voltage, application studies on the organic lightemitting device for forming devices, including material development,have been made actively.

For example, as is described in detail in Micromol. Symp. 125, 1-48(1997), an organic electroluminescence (EL) device, which is arepresentative example of the organic light emitting device, hasgenerally a structure in which upper and lower electrodes, and anorganic layer including a light emitting layer formed between theelectrodes are provided on a transparent substrate. The basicconstitution thereof is shown in FIGS. 1A and 1B.

As shown in FIGS. 1A and 1B, an organic EL device is generally composedof a transparent electrode 14 and a metal electrode 11 on a transparentsubstrate 15, and a plurality of organic layers disposed between theelectrodes. Like features in the respective figures are indicated withlike numerals.

In FIG. 1A, an organic layer consists of a light emitting layer 12 and ahole transport layer 13. As the material for the transparent electrode14, a material with a large work function, such as ITO, is used toachieve good hole-injecting characteristics from the transparentelectrode 14 to the hole transport layer 13. As the material for themetal electrode 11, a material with a small work function, such asaluminum, magnesium and alloys thereof, is used to achieve goodelectron-injecting characteristics to the organic layer. Theseelectrodes generally have a thickness of 50-200 nm.

For the light emitting layer 12, an aluminoquinolinol complex (arepresentative example is Alq3 shown in the following chemical formulasI) or the like is used. As the hole transport layer 13, for example, anelectron-donating material such as a biphenyldiamine derivative (arepresentative example is α-NPD shown in the following chemical formulasI) is used.

The organic EL device constructed as described above has a rectifyingproperty, and when an electric field is applied so as to make the metalelectrode 11 act as a cathode and the transparent electrode 14 act as ananode, electrons are injected from the metal electrode 11 into the lightemitting layer 12, and holes are injected from the transparent electrode14 into the light emitting layer 12.

When the injected holes and electrons recombine in the light emittinglayer 12, excitons are formed, and light is emitted in the process ofthe radiation and deactivation of these excitons. At this time, the holetransport layer 13 plays the role of an electron blocking layer to raisethe recombination efficiency in the light emitting layer 12/holetransport layer 13 interface, and to enhance light emitting efficiency.

Furthermore, in FIG. 1B, an electron transport layer 16 is formedbetween the metal layer 11 and the light emitting layer 12 of FIG. 1A.Thus, by independently forming the electron transport layer 16 toisolate the light emitting function from the electron/hole transportfunction, and making more effective carrier blocking constitution,efficient light emitting can be performed. As the material for theelectron transport layer 16, for example, an oxadiazole derivative orthe like can be used.

Heretofore, in light emission generally used in the organic EL device,the excited state includes an excited singlet state and an excitedtriplet state. A light emission accompanying a transition from theformer state to a ground state is referred to as fluorescence, while alight emission accompanying a transition from the latter state to aground state is referred to as phosphorescence; and substances in thesestates are referred to as a singlet exciton and a triplet exciton,respectively.

Many of the organic light emitting devices so far studied utilizefluorescence generated in transition from the singlet exciton to aground state. Recently, on the other hand, devices that utilizephosphorescence through triplet exciton have been studied.

The representative documents published concerning the results of suchstudies are: Document 1: D. F. O'brien et al., “Improved energy transferin Electrophosphorescent device”, Applied Physics Letters Vol. 74, No.3, p. 422 (1999); and document 2: M. A. Baldo et al., “Veryhigh-efficiency green organic light-emitting devices based onElectrophosphorescence”, Applied Physics Letters Vol. 75, No. 1, p. 4(1999).

In these documents, as shown in FIG. 1C, an organic layer of a four (4)layer structure is mainly used. In this structure, a hole transportlayer 13, a light emitting layer 12, an exciton-diffusion preventinglayer 17 and an electron transport layer 16 are stacked in the namedorder from the anode side. The materials used therein are carriertransport materials and phosphorescent materials shown in the followingchemical formulas I. The term “phosphorescent material” used herein isintended to mean a material having phosphorescent properties at around20° C.

The abbreviations of materials in the following chemical formulas Istand for the following means:

-   Alq3: aluminoquinolinol complex;-   α-NPD:    N4,N4′-di-naphthalen-1-yl-N4,N4′-diphenyl-biphenyl-4,4′-diamine;-   CBP: 4,4′-N,N′-dicarbazole-biphenyl;-   BCP: 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline;-   Bphen: 4,7-diphenyl-1,10-phenanthroline;-   PtOEP: platinum-octaethylporphyrine complex; and-   Ir(ppy)3: Iridium-phenylpyridine complex.

Devices that showed high light-emitting efficiencies in both Documents 1and 2 were constituted by using α-NPD as the hole transport layer 13,Alq3 as the electron transport layer 16, and BCP as theexciton-diffusion preventing layer 17; and the light emitting layer 12was constituted using CBP as the host material, and incorporating PtOEPor Ir(ppy)3 as a phosphorescent material in a concentration of about 6%thereinto.

The reason why the phosphorescent material particularly attractattention is that a high light emitting efficiency can be theoreticallyexpected. Specifically, excitons formed by the recombination of carriersconsist of singlet excitons and triplet excitons, and the probability ofthe formation thereof is 1:3. Although conventional organic EL devicesutilized fluorescence during the transition from the singlet excitonstate to the ground state as light emission, the light emitting yieldwas theoretically 25% relative to the number of formed excitons, andthis was the theoretical upper limit. However, if phosphorescence fromexcitons generated from the triplet state is used, at least 3-fold yieldis theoretically expected, and when the transfer by the intersystemcrossing from the singlet state of a high energy level is considered,4-fold, that is 100%, light emitting efficiency can be theoreticallyexpected.

International Publication No. WO 02/02714 discloses an example of adevice using a fluorine-containing compound in a light emitting layer,and reports that use of a fluorinated material only as a guest material,which is a material that contributes to light emission, inhibitedlowering of the light emitting efficiency even if the content of theguest material was elevated, compared with the case wherein anon-fluorinated material was used.

The light emission lifetime of an organic light emitting device isaffected by factors, such as the glass transition temperature and thestability to electric charge of the material for the charge transportlayer and the light emitting material, and the interfacial state betweenlayers; and furthermore, in the host-guest light emitting layer whereintwo or more components of conductive host materials and light emittingguest materials are mixed, by various factors, such as thedispersibility and the content of each organic material, stabilityduring vapor deposition, and moisture content.

Thus, there are generally a large number of factors affecting thelifetime of an organic light emitting device. Therefore, there is acontinuing need for a device constitution that enables the elongation ofthe lifetime of organic light emitting devices.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide anorganic light emitting device that has a high light emitting efficiencyand a long light emission lifetime.

According to the present invention, there is provided an organic lightemitting device comprising a pair of electrodes provided on a substrate,and a light emitting layer comprising at least one layer of an organicsubstance provided between the electrodes, wherein the light emittinglayer comprises a first organic substance and a second organic substancemainly concerning a light emission wavelength of the light emittinglayer, and wherein the first organic substance comprises afluorine-containing organic compound.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B and 1C are schematic vies each showing an example of theconstitution of an organic light emitting device of the presentinvention;

FIG. 2 is a partly broken perspective view showing the constitution ofthe simple matrix type organic EL device of Example 14;

FIG. 3 is a diagram showing drive signals of the simple matrix typeorganic EL device of Example 14;

FIG. 4 is a schematic diagram showing an example of a panel constitutionequipped with an organic EL device and a drive means;

FIG. 5 is a diagram showing an example of a pixel circuit; and

FIG. 6 is a schematic view showing an example of a cross-sectionalstructure of a TFT substrate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The term “fluorine-containing organic compound” used herein is intendedto mean an organic compound that contains at least one fluorine atom inone molecule thereof, or when it is a polymer compound, an organicpolymer compound that contains at least one fluorine atom in onerepeating unit (monomer unit) thereof, and is hereinafter sometimesabbreviated as “fluorine-containing compound” as needed.

In the present invention, it is preferred that the chemical structure ofthe first organic compound is characterized by containing a singlefluorine atom in one molecule of the organic substance, or havingfluorine atoms in one molecule thereof.

Further, it is preferred that the second organic substance comprises aphosphorescent organic compound.

Moreover, it is preferred that the content of fluorine in the firstorganic substance is 1% by weight or more.

In addition, it is preferred that both the first organic substance andthe second organic substance contain fluorine, or that each of the firstorganic substance and the second organic substance is composed of pluralkinds of organic substances and each molecule of all the organiccompounds contains at least one fluorine atom.

In order to prolong the lifetime of an organic EL device, it is needlessto say that the stability of an organic compound itself that composesthe device is important. However, there are also problems of how totransfer an energy between hosts or between a host and a guestefficiently, or how to prevent mixing by mutual diffusion between alight emitting layer and a charge transfer layer to inhibit transfer ofan excitation energy to a charge transfer layer. Further, as the organiccompound to be used, it can be said that a compound having goodvapor-deposition properties and high hydrophobicity is ideal. Between ahost and a guest, it can be considered that good matching of the hostwith the guest, for example, better dispersibility, is preferable toinhibit degradation with the elapse of time from initialcharacteristics.

For these reasons, the present inventors have found that the prolongedlife could be realized by the use of a fluorine-containing compound forthe light emitting portion.

According to such a constitution of the present invention, by the use ofa fluorine-containing compound in the light emitting layer, thestability of the device is improved. This is considered for thefollowing reasons.

Namely, when fluorine atoms are incorporated in a molecule of acompound, the sublimation temperature of the compound lowers andsublimation becomes easier, shortening the vapor deposition time, orenabling stable vapor deposition, and decomposition during vapordeposition is inhibited. Since a fluorine atom has lower affinity towater than a hydrogen atom, incorporation of water is inhibited, andwhen compared with equivalent compounds that do not contain fluorineatoms, incorporation of water during storage or vapor deposition can beinhibited.

Moreover, it is considered as a further effect that since afluorine-containing compound is difficult to mix not only with water,but also with ordinary compounds that do not contain halogen atoms,mixing of layers due to mutual diffusion between a transport layer and ablocking layer in a light emission interface is difficult to occur, andthe deactivation of an energy due to layer mixing in a light emittingportion can be inhibited.

Furthermore, it is considered that when a fluorine-containing compoundis used as a guest in a layer of a host-guest structure, if afluorine-containing compound is used also as the host, thedispersibility of the guest is improved, and degradation due toaggregation is inhibited, compared with a case wherein a compound thatdoes not contain fluorine is used as the host.

In fact, the present inventors have found that when afluorine-containing compound is used as a guest in a layer of ahost-guest structure, further when a fluorine-containing compound isused also as the host, the degradation with the elapse of time isretarded, compared with a case where a compound that does not containfluorine is used as the host.

Although the above-described constitution of the present invention ischaracterized by allowing a molecule of a compound to contain fluorine,since a change in an energy gap of the compound occurs by incorporatingfluorine atoms in the molecule, that is, since an absolute value ofHOMO/LUMO increases to improve the electron affinity, theabove-described fluorine-containing compounds can be considered to be amaterial with improved electron transportation characteristics, and canbe utilized not only in a light emitting layer, but also in othertransport layers and the like.

For the reasons described above, according to the constitution of thepresent invention, a light emitting material suited for prolongation ofthe lifetime of a light emitting device.

Also in the present invention, for the purpose of preventing the mixingof the layers due to the mutual diffusion as described above, afluorine-containing compound can further be used as the material of alayer adjacent to the light emitting layer.

Furthermore, when the constitution as a device is considered, the use ofa fluorine-containing compound in any one of the other layers inaddition to the light emitting layer can effectively inhibitincorporation of water, and use of a fluorine-containing compound in allthe layers can prolong the lifetime.

The incorporation of fluorine in the layers can be realized by using afluorine-containing compound in some or all of the organic substancesused for the fabrication of the layers.

The following general formulas (1) are examples of fluorine-containingorganic compounds included by the first organic substance of the presentinvention.

As the second organic substance that mainly concerns the light emissionwavelength of the light emitting layer, there are included fluorescentmaterials, phosphorescent materials and the like that emit light when anelectric charge is imparted. In the case of phosphorescent materials, itis preferable to use a metal complex having atoms of copper (Cu),rhenium (Re), ruthenium (Ru), rhodium (Rh), thulium (Tm), iridium (Ir),platinum (Pt), gold (Au), etc. as the metal center or the like, but thepresent invention is not limited to these metals.

The following general formulas (2) are examples of compounds that can beused as the second organic substance.

It is preferable that the organic light emitting device of the presentinvention is an electroluminescent device (EL device) of a structure asshown in FIGS. 1A to 1C, wherein a fluorine-containing organic compoundlayer is sandwiched by two opposing electrodes, and light is emitted byapplying a voltage between the electrodes.

EXAMPLES

The present invention will be specifically described below referring toexamples.

Example 1

In this example, a device of a device constitution having three organiclayers was fabricated. After forming an ITO film (transparent electrode14) of a thickness of 100 nm on a glass substrate (transparent substrate15), the film was patterned in stripes in accordance in the usual way.The following organic layers and electrode layers of the followingthicknesses were formed using the following material substances on theITO film by vacuum vapor deposition using the resistance heating methodin a vacuum chamber of 10⁻⁴ Pa.

-   -   Organic layer 1 (hole transport layer 13): film thickness 40 nm:        material substance HT-A;    -   Organic layer 2 (light emitting layer 12): film thickness 20 nm:        material substance EH-A (92% by weight)/EG-A (8% by weight);    -   Organic layer 3 (electron transport layer 16): film thickness 50        nm: material substance Bphen;    -   Metal electrode layer 1: film thickness 1 nm: material substance        KF; and    -   Metal electrode layer 2: film thickness 100 nm: material        substance Al

The metal electrode layers 1 and 2 were formed so as to be perpendicularto the ITO electrodes, and equally patterned in stripes so that theopposing area of the electrodes becomes 3 mm².

The chemical structures of the substances used in forming each organiclayer are shown in the following chemical formulas II.

Comparative Example 1

A device was fabricated following the same procedure as in Example 1,with the exception that EH-B of the following structure was used inplace of EH-A used for the organic layer 2 in Example 1.

Example 2

A device was fabricated following the same procedure as in Example 1,with the exception that EH-C of the following structure was used inplace of EH-A used for the organic layer 2 in Example 1.

Example 3

A device was fabricated following the same procedure as in Example 1,with the exception that EH-D of the following structure was used inplace of EH-A used for the organic layer 2 in Example 1.

Comparative Example 2

A device was fabricated following the same procedure as in Example 1,with the exception that CBP described above was used in place of EH-Aused for the organic layer 2 in Example 1.

Example 4

A device was fabricated following the same procedure as in Example 1,with the exception that EH-E of the following structure was used inplace of EH-A used for the organic layer 2 in Example 1.

Comparative Example 3

A device was fabricated following the same procedure as in Example 1,with the exception that EH-F of the following structure was used inplace of EH-A used for the organic layer 2 in Example 1.

Example 5

A device was fabricated following the same procedure as in Example 1,with the exception that EG-B of the following structure was used inplace of EG-A, and EH-E was used in place of EH-A used for the organiclayer 2 in Example 1.

Example 6

A device was fabricated following the same procedure as in Example 1,with the exception that EG-C of the following structure was used inplace of EG-A used for the organic layer 2 in Example 1.

Example 7

A device was fabricated following the same procedure as in Example 1,with the exception that EG-D of the following structure was used inplace of EG-A used for the organic layer 2 in Example 1.

An electric field was applied to each of the devices fabricated inExamples 1 to 7 and Comparative Examples 1 to 3 so that the ITO(transparent electrode 14) became an anode, and Al (metal electrode 11)became a cathode, and the light emission lifetime of each device wasmeasured. Specifically, the luminance was set to about 1,000 cd/cm², andthe half-value period of luminance was measured under a constantcurrent. Since the presence of oxygen or water poses a problem as acause of the degradation of a device, in order to remove the cause, theabove measurement was performed in a dry nitrogen flow after the devicewas taken out of the vacuum chamber.

The results obtained for each device are shown in Table 1. TABLE 1Half-value period of luminance (h) Example 1 15 Comparative 0.2 Example1 Example 2 10 Example 3 40 Comparative 0.1 Example 2 Example 4 14Comparative 0.5 Example 3 Example 5 17 Example 6 15 Example 7 4

It was confirmed from the results shown in Table 1 that in the case ofusing a fluorine-containing guest, when a host not containing fluorinewas used, the half-value period of luminance was very short; however,when a fluorine-containing host was used, the half-value period ofluminance elongated several to several hundred times. Further, when acombination of a fluorine-containing host and a guest not containingfluorine was used, substantially the same effect as in afluorine-containing host/fluorine-containing guest combination.

Example 8

A device was fabricated following the same procedure as in Example 1,with the exception that a combination of EH-D and CBP wherein thefluorine content in the total quantity thereof was adjusted to be 1% byweight was used in place of EH-A used for the organic layer 2 in Example1 to perform the vapor deposition.

Example 9

A device was fabricated following the same procedure as in Example 1,with the exception that a combination of EH-D and CBP wherein thefluorine content in the total quantity thereof was adjusted to be 10% byweight was used in place of EH-A used for the organic layer 2 in Example1 to perform the vapor deposition.

Comparative Example 4

A device was fabricated following the same procedure as in Example 1,with the exception that a combination of EH-D and CBP wherein thefluorine content in the total quantity thereof was adjusted to be 0.1%by weight was used in place of EH-A used for the organic layer 2 inExample 1 to perform the vapor deposition.

An electric field was applied to each of the devices fabricated inExamples 8 and 9 and Comparative Example 4 so that the ITO (transparentelectrode 14) became an anode and Al (metal electrode 11) became acathode, and the light emission lifetime was measured. Specifically, theluminance was set to about 1,000 cd/cm², and the half-value period ofluminance was measured under a constant current. Since the presence ofoxygen or water poses a problem as the cause of the degradation of adevice, in order to remove the cause, the above measurement wasperformed in a dry nitrogen flow after the device was taken out of thevacuum chamber.

The results obtained for each device are shown in Table 2. TABLE 2Half-value period of luminance (h) Example 8 5 Example 9 15 Comparative0.5 Example 4

Example 10

A device was fabricated following the same procedure as in Example 1,with the exception that a combination of EG-A and EG-B wherein thefluorine content in the total quantity thereof was adjusted to be 1% byweight was used in place of EG-A used for the organic layer 2 in Example1 to perform the vapor deposition; and furthermore, a combination ofEH-D and CBP wherein the fluorine content in the total quantity thereofwas adjusted to be 1% by weight was used in place of EH-A to perform thevapor deposition.

Comparative Example 5

A device was fabricated following the same procedure as in Example 1,with the exception that a combination of EG-A and EG-B wherein thefluorine content in the total quantity thereof was adjusted to be 1% byweight was used in place of EG-A used for the organic layer 2 in Example1 to perform the vapor deposition; and furthermore, a combination ofEH-D and CBP wherein the fluorine content in the total quantity thereofwas adjusted to be 0.1% by weight was used in place of EH-A to performthe vapor deposition.

An electric field was applied to each of the devices fabricated inExample 10 and Comparative Example 5 so that the ITO (transparentelectrode 14) became an anode and Al (metal electrode 11) became acathode, and the light emission lifetime was measured. Specifically, theluminance was set to about 1,000 cd/cm², and the half-value period ofluminance was measured under a constant current. Since the presence ofoxygen or water poses a problem as the cause of the degradation of adevice, in order to remove the cause, the above measurement wasperformed in a dry nitrogen flow after the device was taken out of thevacuum chamber.

The results obtained for each device are shown in Table 3. TABLE 3Half-value period of luminance (h) Example 10 8 Comparative 0.3 Example5

Example 11

In this example, a device of a device constitution having two organiclayers shown in FIG. 1A was fabricated. As in Example 1, after formingan ITO film (transparent electrode 14) of a thickness of 100 nm on aglass substrate (transparent substrate 15), the film was patterned instripes in the usual way. The following organic layers and electrodelayers of the following thickness were sequentially formed using thefollowing material substances on the ITO film by vacuum vapor depositionusing the resistance heating method in a vacuum chamber of 10⁻⁴ Pa.

-   -   Organic layer 1 (hole transport layer 13): film thickness 50 nm:        material substance EH-C;    -   Organic layer 2 (light emitting layer 12): film thickness 50 nm:        material substance EH-E (92% by weight)/EG-A (8% by weight);    -   Metal electrode layer 1: film thickness 1 nm: material substance        KF; and    -   Metal electrode layer 2: film thickness 100 nm: material        substance Al

The metal electrode layers 1 and 2 were formed so as to be perpendicularto the ITO electrodes, and equally patterned in stripes so that eachopposing area of the electrodes becomes 3 mm².

When an electric field was applied to the fabricated device with the ITOside used as the anode and the Al side used as the cathode, the emissionof red light derived from EG-A was confirmed.

Example 12

Through the synthesis route shown below, PEH-A (Mn=150,000; Mw/Mn=2.3(in THF, in terms of polystyrene standard)) was synthesized.

An organic EL device having three organic layers of the constitutionshown in FIG. 1B was fabricated, and the device characteristics weremeasured. An alkali-free glass substrate was used as the transparentelectrode 15, an indium oxide (ITO) film of a thickness of 100 nm wasformed thereon as the transparent electrode 14 using the sputteringmethod, and the ITO film was subjected to patterning.

A high-polymer film consisting of PEDOT and PSS shown in the abovestructural formulas of a film thickness of 30 nm was formed thereon asthe hole transport layer 13 by the spin-coating method. A 1.0%chloroform solution of powder formed by mixing PEH-A and EG-A in theweight ratio of 10:1 was spin-coated plural times thereon as the lightemitting layer 12, and dried for 60 minutes in an oven at 60° C. toobtain the light emitting layer 12 of a film thickness of 30 nm.Furthermore, as the electron transport layer 16, Bphen having the abovestructure was resistance-heated under a vacuum of 10⁻⁴ Pa tovapor-deposit an organic film of a film thickness of 40 nm.

Thereon, potassium fluoride KF was disposed as an underlying layer ofthe metal electrode 11. Furthermore, as the metal electrode 11, analuminum (Al) film of a film thickness of 100 nm was vapor-depositedthereon, and patterned in a form so that the area of the electrodeopposing the transparent electrode 14 becomes 3 mm².

As the characteristics of the fabricated EL device, the current-voltagecharacteristics were measured using Hewlett Packard 4140B Pico-ampmeter, and light-emission luminance was measured using Topcon BM7luminance colorimeter. As a result, the device fabricated using thecompounds of this example exhibited good rectification properties.

When a voltage of 15 V was applied, light emission from the EL device ofthis example was confirmed. In this example, emission of red lightappearing to be derived from EG-A was confirmed.

Example 13

A device was fabricated following the same procedure as in Example 12,with the exception that EG-B was used in place of EG-A used for theorganic layer in Example 12.

Comparative Example 6

A device was fabricated following the same procedure as in Example 12,with the exception that PVK of the following structure was used in placeof PEH-A used for the organic layer in Example 12.

An electric field was applied to each of the devices fabricated inExamples 12 and 13 and Comparative Example 6 so that the ITO(transparent electrode 14) became an anode and Al (metal electrode 11)became a cathode, and the light emission lifetime was measured.Specifically, the luminance was set to about 1,000 cd/cm², and thehalf-value period of luminance was measured under a constant current.Since the presence of oxygen or water poses a problem as the cause ofthe degradation of a device, in order to remove the cause, the abovemeasurement was performed in a dry nitrogen flow after the device wastaken out of the vacuum chamber.

The results obtained for each device are shown in Table 4. TABLE 4Half-value period of luminance (h) Example 12 18 Example 13 15Comparative 2 Example 6

Example 14

In this example, two examples of image display apparatuses will bedescribed.

First, an example of fabrication of an image display apparatus having anXY matrix such as shown in FIG. 2 will be described.

After forming an ITO film of a thickness of about 100 nm as atransparent electrode 22 (anode side) by the sputtering method on aglass substrate 21 of a length of 150 mm, a width 150 mm and a thicknessof 1.1 mm, 100 lines were patterned at a distance of line/space=100μm/40 μm as simple matrix electrodes. Next, under the same conditions asin Example 1, the same organic compound layers 23 as those fabricated inExamples 1 to 7 were formed, respectively.

Then, metal electrodes 24 (cathode side) for 100 lines of line/space=100μm/40 μm were formed so as to be perpendicular to the transparentelectrodes by the vacuum vapor deposition method under the vacuumcondition of 2×10⁻⁵ Torr. As the metal electrodes, an Al/Li alloy (Li:1.3% by weight) of a film thickness of 10 nm, and then, Al of a filmthickness of 150 nm were formed.

This 50×50 simple-matrix-type organic EL device was placed in a glovebox filled with a nitrogen atmosphere, and simple matrix-driven using ascanning signal of 10 V and an information signal of ±3 V shown in FIG.3 at a voltage from 7 V to 13 V. By interlace driving at a framefrequency of 30 Hz, light emitting images were confirmed in therespective devices.

According to the light emitting device of a high light emittingefficiency of the present invention, as an image display apparatus, alightweight flat-panel display with energy saving performance and highvisibility can be provided. As a light source for printers, utilizationas a line shutter can be attained by forming the light emitting devicesof the present invention in a line, disposing the devices in thevicinity of a photosensitive drum, and driving each device independentlyto perform a desired exposure to the photosensitive drum. On the otherhand, when it is utilized as a backlight of illumination apparatuses orliquid crystal displays, energy-saving effect can be expected.

As another example of the image display apparatus, an active matriximage display apparatus equipped with thin film transistors (TFTs) inplace of the above-described XY matrix wiring is particularly useful. Anactive matrix image display apparatus to which the present invention isapplied will be described below referring to FIGS. 4 to 6.

FIG. 4 is a schematic plan view of the above-described device panel.Around the panel are disposed a drive circuit consisting of a scanningsignal driver and a current supply source, and a display-signal inputmeans, which is an information signal driver (these are referred to as“image information supply means”), each of which is connected toX-direction scanning lines called gate lines, Y-direction wirings calledinformation lines, and current supply lines. The scanning signal driverselects the gate scanning lines sequentially, and image signals aresupplied from the information signal driver synchronizing therewith.Pixels for display are disposed on the intersections of the gatescanning lines and information lines.

Next, the operation of the pixel circuit will be described using theequivalent circuit shown in FIG. 5. Now, when a selection signal isapplied to the gate selecting line, TFT1 is turned on and a displaysignal is supplied from the information signal line to a capacitor Caddto determine the gate potential of TFT2. To the organic EL deviceportion disposed in each pixel is supplied a current from the currentsupply line depending on the gate potential of TFT2. Since the gatepotential of TFT2 is retained in Cadd during one frame period, thecurrent from the current supply line continues to flow in the EL deviceportion during this period. Thereby, light emission can be maintainedduring one frame period.

FIG. 6 is a schematic view of a cross-sectional structure of a TFT usedin this example. A polysilicon (p-Si) layer 62 is formed on a glasssubstrate 61, and a channel region 63, a drain region 64 and a sourceregion 65 are doped with necessary impurities. A gate electrode 67 isformed thereon through a gate insulating layer 66, and a drain electrode68 and a source electrode 69 connected to the drain region and thesource region are formed, respectively. In this case, the drainelectrode 68 is connected to a transparent pixel electrode (ITO) 70through a contact hole 72 made in an insulating layer 71 that intervenesbetween them.

There is no limitation in the active devices used for the device of thepresent invention, and a single-crystal silicon TFT, an amorphoussilicon (a-Si) TFT and the like can also be used.

A multi-layer or single-layer organic light emitting layer 73 can beformed on the above-described pixel electrode, and a metal electrode 74,which is a cathode, can be stacked sequentially to obtain an activeorganic light emitting display device.

According to the present invention, as described above, an organic lightemitting device having a long device lifetime can be obtained. Theorganic light emitting device of the present invention is also excellentas a display device.

Furthermore, since the organic light emitting device of the presentinvention has a high light emitting efficiency, it can be applied tovarious products that require energy saving or high luminance. Examplesof such applications include a light source for display apparatuses,illumination apparatuses, printers and the like; and a backlight forliquid-crystal display apparatuses. When it is applied to displayapparatuses, lightweight flat-panel displays with energy savingperformance and high visibility can be manufactured. When it is appliedto illumination apparatuses or backlights, energy-saving effect can beexpected.

1. An organic light emitting device comprising a pair of electrodesprovided on a substrate, and a light emitting layer comprising at leastone layer of an organic substance and provided between the electrodes,wherein the light emitting layer comprises a first organic substance anda second organic substance that mainly concerns a light emissionwavelength of the light emitting layer, and wherein the first organicsubstance comprises a fluorine-containing organic compound.
 2. Theorganic light emitting device according to claim 1, wherein thefluorine-containing organic compound contains a single fluorine atom ina molecule or repeating unit thereof.
 3. The organic light emittingdevice according to claim 2, wherein the second organic substancecomprises a phosphorescent organic compound.
 4. The organic lightemitting device according to claim 3, wherein the fluorine-containingorganic compound contains a single fluorine atom in a molecule orrepeating unit thereof.
 5. The organic light emitting device accordingto claim 1, wherein the content of fluorine in the first organicsubstance is 1% by weight or more.
 6. The organic light emitting deviceaccording to claim 3, wherein the content of fluorine in the firstorganic substance is 1% by weight or more.
 7. The organic light emittingdevice according to claim 1, wherein the second organic substancecontains fluorine.
 8. The organic light emitting device according toclaim 7, wherein each of the first and the second organic substance iscomposed of plural kinds of organic compounds, and all the organiccompounds contain at least one fluorine atom in a molecule or repeatingunit thereof.
 9. The organic light emitting device according to claim 8,wherein all of the organic compounds contain a single fluorine atom in amolecule or repeating unit thereof.
 10. The organic light emittingdevice according to claim 7, wherein the second organic substancecontains a phosphorescent organic compound.
 11. The organic lightemitting device according to claim 8, wherein the second organicsubstance contains a phosphorescent organic compound.
 12. The organiclight emitting device according to claim 7, wherein the content offluorine in each of the first and the second organic substances is 1% byweight or more.
 13. The organic light emitting device according to claim12, wherein the second organic substance contains a phosphorescentorganic compound.
 14. The organic light emitting device according toclaim 1, wherein the second organic substance contains a phosphorescentorganic compound, and the phosphorescent organic compound contains ametal element selected from the group consisting of Cu, Re, Rh, Pt, Ru,Tm, Ir, and Au, and fluorine.
 15. The organic light emitting deviceaccording to claim 1, wherein the second organic substance contains aphosphorescent organic compound, and the phosphorescent organic compoundcontains iridium and fluorine.
 16. The organic light emitting deviceaccording to claim 1, wherein the first organic substance contains acompound having any one of the structures shown in the general formulas(1) below, and the second organic substance contains a compound havingany one of the structures shown in the general formulas (2) below.


17. The organic light emitting device according to claim 1, furthercomprising another organic substance layer between the electrodes, andall the organic substance layers contain fluorine.